The present invention relates to scrims of woven polyolefin tapes having improved strength. In particular the invention relates to scrims in the form of tarpaulins, lumber covers, or in other forms, that have improved tear strength, and to a method for the manufacture of such scrims.
Scrims are used in a variety of forms, particularly in the transportation industry. For instance, scrims in the form of tarpaulins are widely used in the transportation of goods in order to protect a load of goods on a flat-bed truck or on a rail car against the effects of rain, snow, sun or other environmental or weather situations. For instance, if the load is a stack of lumber, it is important and desirable to protect the stack of lumber from the effects of weather in order to prevent soiling, staining or other damage to the lumber. This is particularly important for finished lumber. Other uses include use as geomembranes and as covers for hoop structures, including hay stacks and temporary buildings, landfill covers, pit and pond liners, heavy duty protective covers and as other covers where tear strength is important.
Such tarpaulins and other covers are known and are typically made of a woven polyolefin fabric in the form of a scrim, especially from tapes of high density polyethylene, polypropylene or other polyolefins. Examples of lumber covers are given in U.S. Pat. No. 4,239,831 of T. W. E. Pattenden, which discloses a cover formed from woven tapes of high density polyethylene. Canadian Patent 1,332,843 of J. Finell et al. discloses a tarpaulin formed from multifilament warp yarns a combination of woven multifilament yarns and flat film yarns as weft yarns. U.S. Pat. No. 3,503,106 of M. I. Port et al. discloses material formed in a continuous process in which tapes are extruded and the edges thereof are folded back on themselves prior to the weaving of the fabric.
While tarpaulins and other covers or scrims formed of woven polyolefin tapes have performed satisfactory in a number of end-uses, it would be desirably to improve the strength of such scrims, especially the tear strength of the scrims, in order to improve the performance of the scrim in use. Such a scrim, and a method for the fabrication thereof, has now been found.
Accordingly, the present invention provides a scrim of woven polyolefin tapes comprising:
a) a plurality of warp tapes in a substantially parallel side-by-side relationship;
b) a plurality of weft tapes in a substantially parallel side-by-side relationship;
c) at least some of each of said warp and said weft tapes being in the form of a tape having at least one of an additional tape and a multifilament yarn superimposed thereon, each of said tapes being a polyolefin tape.
The present invention also provides a scrim of woven polyolefin tapes comprising:
a) a plurality of warp tapes in a substantially parallel side-by-side relationship;
b) a plurality of weft tapes in a substantially parallel side-by-side relationship;
c) each of said warp and said weft tapes being in the form of a tape having at least one of an additional tape and a multifilament yarn superimposed thereon, each of said tapes being a polyolefin tape.
The present invention further provides a method for the fabrication of a scrim of woven polyolefin tapes in which said polyolefins tapes are fed to a loom for fabrication of a scrim of warp and weft tapes in a substantially parallel side-by-side relationship, comprising feeding to said loom at least one of an additional tape or a multifilament yarn with at least some of said warp and said weft tapes, said additional tape and said multifilament yarn being superimposed on said warp and said weft tapes and being woven therewith in said loom.
The present invention also provides a method for the fabrication of a scrim of woven polyolefin tapes in which said polyolefins tapes are fed to a loom for fabrication of a scrim of warp and weft tapes in a substantially parallel side-by-side relationship, comprising feeding to said loom at least one of an additional tape or a multifilament yarn with each of said warp and said weft tapes, said additional tape and said multifilament yarn being superimposed on said warp and said weft tapes and being woven therewith in said loom.
In a preferred embodiments of the present invention, the ratio of the tear strength in the warp direction to the tear strength in the weft direction is in the range of 2:1 to 1:2, especially in the range of 1.5:1 to 1:1.5.
In other embodiments, the multifilament yarn is selected from polyethylene, polypropylene, polyamide and polyester multifilament yarn.
In further embodiments, the warp and weft tapes have tapes superimposed thereon, or alternatively have multifilament yarn superimposed thereon.